Cot Bed and Children's Mattress Sizes

For a cot mattress, fit is a safety matter rather than a comfort one. The gap between the mattress and the cot side is the number that counts, and the guidance is that it should be no more than 3 cm anywhere around the edge.

This page covers sizes and fit. For anything about safe sleep for a baby, the Lullaby Trust and the NHS are the sources to use — not a mattress retailer, us included.

The standard sizes

Bed	Usual mattress size	Age range
Crib / Moses basket	Varies widely — always measure	0–6 months
Cot	120 × 60 cm	0–18 months
Cot bed	140 × 70 cm	0–4 years
Continental cot bed	140 × 70 or 120 × 60 cm	0–4 years
Toddler bed	140 × 70 cm	2–5 years
Small single	75 × 190 cm	4+ years
Single	90 × 190 cm	5+ years

Cribs and Moses baskets are the exception — there is no standard at all and many are oval or tapered. Measure the base, or template it.

Measure the cot, not the old mattress

Same rule as for adult beds, and it matters more here. Measure the internal length and width of the cot base at its narrowest point. The mattress should fill it with no more than 3 cm of gap at any edge, and it should not have to be forced in — a mattress compressed to fit will bow upward in the middle.

Firmness: the opposite of adult advice

Everything on this site about matching firmness to sleeping position applies to adults. For infants it does not. Safe sleep guidance is consistent that a baby's mattress should be firm and flat, with no soft topper, no pillow and no padding added on top.

For an older child in a single bed, ordinary rules resume — a medium suits most children, and a light child needs a softer surface than the rating suggests, exactly as a light adult does.

Fire safety and labelling

Children's mattresses fall under the same Furniture and Furnishings (Fire) (Safety) Regulations 1988 as everything else, with a permanent Schedule 7 label sewn into the border. A mattress with no label should not go into a child's bed.

Waterproofing without smothering the mattress

The practical problem in a child's bed. A solid PVC sheet stops liquids and also stops the mattress breathing, which produces condensation underneath. A cotton protector with a breathable membrane does both jobs — see our cotton protector.

What we make

We do not stock cot or cot bed mattresses as standard sizes. We do cut to any rectangle from 40 × 60 cm upward, which covers cot, cot bed and any non-standard crib — made to measure. For a child moving into a proper bed, a Small single or Single from the main range is the usual step.

Common questions

Can a cot mattress be second hand?

Safe sleep guidance advises a new, firm, flat mattress for each baby where you can. Ask the Lullaby Trust rather than us.

Foam or sprung for a cot bed?

Both are used. Firm and flat matters more than which.

When does a child move to a single?

Usually somewhere between four and six, when they outgrow 140 cm of length.